Sail craft

ABSTRACT

A device for increasing the motive force of a sail acting on a sail craft and at the same time decrease the risk of having the craft turned bottom up after a capsizing are obtained by fastening to the uppermost portion of the sail (3) a certain amount of flexible buoyancy foam (8) which is shaped such as to form together with the mast (1) and the sail (3) an efficient airfoil profile having a smooth contour. On account of its thickness, this airfoil profile will further counteract the short circuit flow of air from the pressure side to the suction side of the sail. The buoyancy foam (8) has at the same time a volume which is large enough to keep the sail (3) and the mast (1) floating at the water surface after a capsizing of the craft. In order to make the folding of the sail (3) easier prior to putting it into a sail bag, the buoyancy foam may be split up into a plurality of buoyancy zones separated by folding zones.

FIELD OF THE INVENTION

The invention relates to a sail craft having a buoyancy body fastened toat least the upper portion of at least one of its sails.

BACKGROUND OF THE INVENTION

From U.S. Pat. No. 3,016,860 a sail boat is known, which has at theuppermost portion of the main sail an inflatable air bag which isinflated automatically like a balloon, when the boat capsizes. However,this air bag will produce a large air resistance when inflated andtherefore cannot be used during normal sailing.

From Swiss patent specification No. 603 392 a windsurfer is known, bywhich the sail is provided with a buoyancy body consisting of a bagcontaining buoyancy material and being adapted to be folded around theuppermost portion of the mast and buttoned on to the sail, e.g. by meansof press fasteners. A device of this kind cannot be used by sailingdinghies and keel boats, the sails of which are hoisted and lowered bymeans of a halyard. In addition, the mast, the buoyancy body and thesail form together a clumsy profile having a large "drag" and a small"lift".

SUMMARY OF THE INVENTION

It is the object of the invention to improve the buoyancy body in suchway that it will permit hoisting and lowering of the sail in the usualway by means of a halyard, will produce an aerodynamically advantageousshape of the mast, the buoyancy body and the sail, taken in combination,and will also produce an "end plate effect", which will appreciablyreduce the short circuit flow of air from the pressure side to thesuction side of the sail across the upper portion of the sail, whereby,in addition, a much better aerodynamical efficiency of the main portionof the sail below the buoyancy body is obtained.

This is according to the invention obtained by the fact that thebuoyancy body is made up of flexible foam material being attached toboth sides of a single layer sail but having no connection with themast, the foam material being shaped such as to form together with thesail and the mast an airfoil profile being as efficient as possible.

As the foam material has no connection whatsoever with the mast, but isattached to the sail only, it will be possible to hoist and lower thesail in the usual way by means of a halyard, and because the foammaterial is shaped in the said manner, the mast, the foam material andthe sail will together form an effective airfoil profile having a ratherlarge lift and a small drag. The front portion of the foam material willhave a relatively large thickness, as its surface has to be flush withthe surface of the mast in order to form the said airfoil profile, sothat the foam material will have a comparatively broad, downward turnedsurface acting as an effective end plate at the upper portion of thesail. Thereby, the main portion of the sail below the foam material willacquire a greatly improved aerodynamical efficiency, because the ratiolift/drag will increase considerably on account of the end plate, as isknown per se. These improvements in combination will result in anappreciable increase of the motive power produced by the sail.Measurements have indicated an increase of up to 85%.

At the same time the sail craft has been safeguarded against180°--capsizings by means of the buoyancy force acting on the buoyancybody, when this is partially submerged after a capsizing.

In order to obtain an advantageous thickness ratio of the airfoilprofile (in the range from 6-12%), the buoyancy material may be shapedsuch as to fill up the two outwardly open spaces between the mast andthe two sides of the sail and to stretch right from the mast to the aftedge of the sail.

A larger flexibility of the buoyancy body, so that this may be camberedby the force of the wind, can be obtained, if the foam material is madeup of a number of thin, flexible plastic foam sheets being laid flat ontop of each other.

In order to make a folding of the buoyancy body possible, when the sailis put into a sail bag, the buoyancy material may be split up intohorisontal sections preferably extending right from the mast to the aftedge of the sail and being separated from each other by folding zones.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be described further in the following with referenceto the drawing, in which

FIG. 1 is a side view of a conventional Bermuda sail, the uppermostportion of which is provided with buoyancy material according to theinvention, and

FIG. 2 on a much larger scale is a section along the line II--II in FIG.1.

The sail 3 shown in FIG. 1 consists of a single layer and is in aconventional manner along the forward edge and lower edge provided witha rope which can be inserted into grooves in a mast 1 and a boom 2,respectively. The uppermost portion of the sail 3 is split up into twobuoyancy zones 4 and 5 being separated by a narrow folding zone 6.

As shown in FIG. 2, the foreleech 7 of the sail is received in a groovealong the aft edge of the mast 1 which consists of a profile obtainableon the market. At both sides of the sail 3 is fastened buoyancy material8 consisting of for example flexible foam plastic which may be foamed upin a mold so that it shall not subsequently be cut to shape. A piece ofsail cloth 9 is laid tightly around the foreleech 7, the two layers ofthe cloth being sewed together closely aft of the foreleech 7. To therear of this seam, the two layers of sail cloth 9 extend along the outersurfaces of the buoyancy material 8 at both sides of the sail 3, and thetwo free edges of the sail cloth 9 are sewed on to the sail 3 by a seam10 along the aft edge of the sail. However, the sail cloth 9 may bedispensed with, if the "skin side" of the buoyancy material 8 is facedoutwardly and is in itself satisfactorily smooth and even.

It will be seen that the buoyancy material 8 is shaped such as to formtogether with the mast 1 and the sail 3 an aerodynamically advantageousprofile having a much better lift/drag ratio than the profiled formed bythe mast 1 and the sail 3 in combination. The thickness ratio of theprofile of section II--II is about 0,25, but further down the thicknessratio will be appreciably smaller. Furthermore, the buoyancy material 8has a volume which is large enough to keep the sail 3 and the mast 1afloat in the water surface after a capsizing of the sail craft on whichthe mast 1 and the sail 3 is mounted.

Instead of foaming up the buoyancy material 8 in the top half a mould asshown in FIG. 2, it is possible to use a plurality of thin layers ofmaterial being laid flat on top of each other and cut to shape toproduce the desired shape as shown in the bottom half of FIG. 2.

It is further possible to attach additional buoyancy material along thewhole length of the forward edge of the sail 3, stretching for examplefrom the mast 1 to the chain-dotted line 11 in FIG. 1. In this way anappreciable decrease of the drag of the sail and a small increase of thelift is obtained. Taken in combination this gives rise to a considerablylarger motive force acting on the sail craft. However, for reasons ofsafety there is no need for this buoyancy material, as the buoyancyzones 4 and 5 are sufficient.

If buoyancy material is placed along the whole length of the forwardedge of the sail, the mast profile should be adapted hereto. The profilemay for instance consist of the front portion of a NACA 0012 bounded atthe rear by a plane surface at right angles to the axis of symmetri ofthe profile. Hereby a still larger motive force of the sail can beobtained than in the case of the profile shown in FIG. 2.

The sail shown in FIGS. 1 and 2 can be used for any sail craft, i.e.also for keel boats, whereby the motive force per square meter of sailarea will be increased by up to 85%, mainly due to the reduction of theshort circuit flow of air from the pressure side to the suction side ofthe sail main portion situated below the thickened buoyancy zones 4 and5.

I claim:
 1. A sail craft having a mast and a thin flat sail attachedthereto, a buoyancy body fastened to as least the upper portion of saidsail, the buoyancy body being made of flexible foam material attached toboth sides of the sail with the foam material being flush with the mastbut having no connection with the mast, the foam material being shapedsuch as to form together with the sail and the mast an air foil profilehaving a smooth uninterrupted surface, with the foam material taperingfrom the mast towards the aft end of the sail.
 2. The sail craft asclaimed in claim 1 having the foam material made up of a number ofvertically oriented, thin, flexible plastic foam sheets being laid flatagainst each other.
 3. The sail craft as claimed in claim 1 having thebuoyancy material split up into horizontal sections preferably extendingfrom the mast to the aft edge of the sail and being separated from eachother by a folding zone.
 4. The sail craft as claimed in claim 1 whereinsaid foam material is formed on its lower edge to present a downwardlyfacing surface being substantially horizontal and at right angles to thesail surface, which acts as an end plate at the upper portion of thesail to appreciably reduce the flow of air from the pressure side to thesuction side of the sail and thereby improve the aerodynamiceffectiveness of the main portion of the sail below the buoyancy body.5. The sail craft as claimed in claim 1 including additional buoyancymaterial along the forward end of the sail below said buoyancy body,said additional buoyancy material conforming to the profile of the rearof said mast and tapering towards the sail to form a smoothuninterrupted profile on each side of the sail.